1. Field of the Invention
The present invention concerns the field of electronic connectors and more specifically an improved cable yoke connector for retaining electrocardiogram or similar plugs against accidental disconnection.
2. Description of Related Art
There is a considerable need for reliable electrical plug connectors particularly in the field of medical testing equipment such as electrocardiogram (ECG) cables and leads. In such tests shielded leads are attached at one end to conductive pads attached at various points on the human body and at another end to lead connector plugs. The plurality of shielded lead connector plugs are then inserted into a common cable yoke socket on a common cable connected to a monitoring instrument. It is important that the various lead connector plugs be readily and securely attached to the yoke plug so that patient movement will not cause an inadvertent disconnection.
As might be imagined, there has been a considerable effort in the industry to produce standardized lead plug and yoke socket design, both to ensure adequate performance of various leads and cable yokes and to allow interchangeability between leads and yokes produced by different manufacturers. To this end an industry/clinician working group, the Association for the Advancement of Medical Instrumentation (AAMI), together with the American Nation Standards Institute (ANSI), has promulgated ANSI/AAMI EC53-1995, a standard for ECG leads, plugs, and yoke sockets. This standard defines the configurations of lead connector plugs and yoke sockets intended to accept those lead connector plugs. The standard allows the manufacturers a certain amount of design leeway as long as the leads and yokes otherwise meet the standard and remain interchangeable. Specifically, while the yoke/lead plug design specified in EC53 does not provide retention means to ensure against inadvertent removal of a lead connector plug from a yoke socket, the standard specifically encourages manufacturers to make modifications designed to provide retention forces to the cable yoke socket/lead plug combination.
The prior art has provided several different designs intended to ensure retention of lead plugs in yoke sockets similar to those used in ECG. For example, U.S. Pat. No. 4,913,667 to Muz describes a lead plug and yoke socket system including a casing intended to reversibly link together a group of lead plugs, as well as a yoke socket equipped with retention force enhancers intended to retain the lead plugs in the yoke socket against accidental disconnection.
In the Muz patent each lead plug is equipped with two separate connectors, one for a signal lead and one for a coaxial shield surrounding the signal lead. These separate connectors are shape-keyed (one round and one square) to ensure correct polarity and are joined by a single basal plug body. The square connector of each pair exhibits a recess or notch intended to interact with force retention enhancers when the connector is inserted into the cable yoke socket. These retention enhancers are provided by a blade stop spring having a free end segment received by the recess.
A potential problem with the blade stop spring is that should the spring become bent or fatigued, it will no longer provide adequate lead plug retention. Furthermore, a common free end segment is provided to interact with the several lead plugs that may be inserted into one cable yoke socket. This arrangement may provide an undesirable degree of mechanical interconnection between the individual lead plugs.
An additional feature in the above-cited Muz patent is a plug combinet which serves to aggregate a set of lead plugs into one convenient unit. Unfortunately, the plug combinet of this invention is a closed unit so that individual plugs are best slipped into the combinet prior to insertion in the yoke socket. However, this can be a clumsy operation since a plurality of plugs and leads must be held in the proper configuration until a lock strip on the combinet is closed.